1. Put a large pot filled halfway with water over high heat; salt it. Peel the potatoes and cut them into 1/2-inch cubes, adding them to the pot as you work.
2. Cover the pot, bring to a boil, and cook, stirring once or twice, until the potatoes are tender enough to pierce with a fork but not mushy, 5 to 15 minutes. Trim and chop the spinach, including the stems.
3. Put 2 tablespoons butter in a large skillet over medium-low heat. Peel 1 inch ginger and 2 cloves garlic; trim the chile. Chop them all together.
4. Add the ginger, garlic, and chile to the skillet and turn the heat to medium-high. Cook, stirring frequently, until the aromatics soften, about 2 minutes. Add 1 tablespoon garam masala or curry powder and a sprinkle of salt; stir until fragrant, less than a minute. Add the spinach a handful at a time if necessary so there’s room as it cooks, and sprinkle with salt and pepper. Cook, stirring occasionally, until the spinach is soft and most of the water boils off, about 5 minutes.
5. When the potatoes are ready, drain them in a colander, reserving about 1 cup cooking liquid. Return the potatoes to the pot, add the spinach mixture, and turn the heat to medium. Add 1 1/4 cups cream. Stir to combine and heat until steaming without coming to a boil, just a minute or two; add some of the reserved potato cooking water if the saag looks dry. Taste and adjust the seasoning, and serve.

— Recipe from How to Cook Everything Fast: Completely Revised and Updated